.\" Copyright (c) Bruno Haible <haible@clisp.cons.org>
.\"
.\" %%%LICENSE_START(GPLv2+_DOC_ONEPARA)
.\" This is free documentation; you can redistribute it and/or
.\" modify it under the terms of the GNU General Public License as
.\" published by the Free Software Foundation; either version 2 of
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.\" References consulted:
.\"   GNU glibc-2 source code and manual
.\"
.TH STRNLEN 3  2020-12-21 "GNU" "Linux Programmer's Manual"
.SH NAME
strnlen \- determine the length of a fixed-size string
.SH SYNOPSIS
.nf
.B #include <string.h>
.PP
.BI "size_t strnlen(const char *" s ", size_t " maxlen );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR strnlen ():
.PD 0
.ad l
.RS 4
.TP 4
Since glibc 2.10:
_POSIX_C_SOURCE\ >=\ 200809L
.TP
Before glibc 2.10:
_GNU_SOURCE
.RE
.ad
.PD
.SH DESCRIPTION
The
.BR strnlen ()
function returns the number of bytes in the string
pointed to by
.IR s ,
excluding the terminating null byte (\(aq\e0\(aq),
but at most
.IR maxlen .
In doing this,
.BR strnlen ()
looks only at the first
.I maxlen
characters in the string pointed to by
.I s
and never beyond
.IR s[maxlen\-1] .
.SH RETURN VALUE
The
.BR strnlen ()
function returns
.IR strlen(s) ,
if that is less than
.IR maxlen ,
or
.I maxlen
if there is no null terminating (\(aq\e0\(aq) among the first
.I maxlen
characters pointed to by
.IR s .
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lb lb lb
l l l.
Interface	Attribute	Value
T{
.BR strnlen ()
T}	Thread safety	MT-Safe
.TE
.SH CONFORMING TO
POSIX.1-2008.
.SH SEE ALSO
.BR strlen (3)
.SH COLOPHON
This page is part of release 5.10 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.